It was an impressive performance, with Santorum winning every income group except those earning more than $200,000 a year, who went for Romney, according to CNN exit polls. He even won a plurality among those who say the economy is the most important issue, usually a Romney strength, CBS found. Romney won among those who placed the most emphasis on electability in November.

The vote puts Santorum back in the winning column after Romney carried Illinois on Tuesday and continues a Southern streak for the former senator.

The outcome adds to the list of states where Romney has performed poorly, despite his frontrunner status, and suggests he was kept off balance by the flap over a top aide comparing his campaign to an Etch a Sketch. (Only 18 percent in a CBS exit poll said the toy story was an important factor in their vote, but it erased Romney’s message for days.)

But the contest drew strikingly little national media attention, even though all four candidates campaigned in Louisiana. Journalistic attention remains heavily focused on whether Romney can win enough delegates to wrap up the nomination before the convention, blunting the impact of any particular state.

Further deflating the primary’s importance is that only 20 of Louisiana’s 46 delegates were at stake in Saturday’s voting.

Still, Santorum’s strong showing in Louisiana could help him resist pressure to fold his campaign and get behind Romney as the inevitable nominee—an argument made most recently by Jeb Bush when he endorsed the former Massachusetts governor. But that endorsement could hardly have been more low-key, and the two have not been campaigning together.

As in most states, the economy was the top issue, cited by just over half of those interviewed in exit polls, with 57 percent saying it is getting worse. And there was something of an enthusiasm gap: 58 percent of Romney voters say they strongly favor him, while 37 percent say they have reservations. Santorum drew 64 percent strong support and 26 percent with reservations.

Louisiana has fewer self-identified evangelicals than Alabama or Mississippi, where Santorum won big, theoretically making it less hostile turf for Romney. But interviews by the Los Angeles Times indicate that many voters were less than receptive to him.

“Before Mitt shakes up his Etch a Sketch again for November, he needs to know he needs to represent conservatives like us,” Michael Nash was quoted as saying.

Santorum had to back away from an attack on Romney two days before the primary that underscored his tendency to push his rhetoric too far. “You win by giving people the opportunity to see a different vision for our country, not someone who is just going to be a little different than the person in there,” Santorum said Thursday. “If they’re going to be a little different, we may as well stay with what we have instead of taking a risk in what may be the Etch a Sketch candidate for the future.”

Some Republicans sharply criticized him for suggesting that four more years of Barack Obama could be preferable to Romney, forcing Santorum to repeat his vow to support the GOP nominee. He tried to deny he had said what he said, telling Fox Business Network this was “a made-up story.”

Romney now moves to more favorable territory. Wisconsin, Maryland, and D.C. vote April 3, and three weeks later it’s New York, Connecticut, Rhode Island, and Delaware, along with Santorum’s home state of Pennsylvania.